Intraocular lenses (IOL) are generally implanted in the eye as a replacement for the natural crystalline lens following cataract surgery or to alter the optical properties of (provide vision correction to) an eye in which the natural lens remains. Intraocular lenses often include an optic, and preferably at least one flexible fixation member or haptic which extends from the optic and becomes affixed in the eye to secure the lens in position. The optic normally includes an optically clear lens. Implantation of such IOLs into the eye involves making an incision in the eye. It is advantageous to have an incision size as small as possible to reduce trauma and speed healing.
IOLs are known which are foldable (deformable) so that the IOL can be inserted through a smaller incision into the eye. A substantial number of instruments have been proposed to aid in inserting such a foldable lens in the eye.
However, whether using a distal loading or proximal loading system, one factor which limits the size of the inserter tube (cartridge) involves the inserter tube itself. For example, the material from which the inserter tube is made (i.e., polypropylene and like polymeric materials) may not be compatible or otherwise susceptible to causing optics (e.g., made from silicone polymeric materials) to pass through relatively small hollow spaces. For example, the injector cartridges may be made of materials, in particular polymeric materials, which have insufficient lubricity to facilitate the passage of a folded IOL through the cartridge.
As a result of this lack of lubricity, the hollow space of the injector cartridge must be made relatively larger to accommodate the folded intraocular lens. This is detrimental because, as noted above, it is advantageous to have the smallest possible incision for insertion of the IOL. In addition, if one were to use a small diameter cartridge to pass the IOL, excessive force might be needed to pass the IOL through the small hollow space thereby increasing the risks of damaging the IOL and, in extreme cases, even damaging the eye into which the IOL is placed.
One approach that may be considered is to use a lubricity agent, for example, such as conventional visco-elastic agents, in the hollow space of the cartridge to facilitate passing the IOL through the insertion apparatus. However, such lubricity agents occupy valuable space, thereby at least partially defeating the purpose of using such agents. Also, such lubricity agents often end up in the eye, thereby creating the risk of causing trauma and/or irritation and/or damage to the eye.
Several different techniques are utilized to apply coatings to the surface of an IOL insertion cartridge. U.S. Pat. No. 5,716,364 issued to Makker et al. on Feb. 10, 1998 (hereinafter the Makker patent, the entire contents of which are incorporated herein by reference) discloses and claims an IOL insertion cartridge fabricated from a hydrophobic structural polymer such as polypropylene. During the manufacturing steps a lubricity enhancing composition such as a fatty acid ester is incorporated into the hydrophobic structural polymer resin. The fabricated cartridge is then subjected to elevated temperatures for a time period that is effective to cause the lubricity enhancing component (for example glycerol monosterate [GMS]) to migrate toward the cartridge's interior surface. A common name for this phenomenon is “blooming.” However, while the bloomed GMS provides an effective lubricious coating, the fatty acid ester continues to deposit on the cartridge surface over time. Consequently, after prolonged storage sufficient GMS can be present on the interior surface of the cartridge such that the IOL becomes streaked with lubricant during the insertion process. Thus, the cartridges' shelf life is less than optimal.
Another method for providing lubricous coatings for IOL insertion cartridges is described in U.S. Pat. Nos. 6,238,799 and 6,866,936, both issued to Opolski on May 29, 2001 and Mar. 15, 2005, respectively (hereinafter the Opolski patents, the entire contents of which are incorporated by reference). The Opolski patents disclose forming interpenetrating networks (IPN) on the surface of hydrophobic structural polymers using a supporting polymer selected from the group consisting of polyacrylates, polymethacrylates, polyurethanes, polyethylene and polypropylene copolymers, polyvinyl chlorides, epoxides, polyamides, polyesters and alkyl copolymers. The supporting polymer is first blended with a hydrophilic polymer selected from the group consisting of poly(N-vinyl lactams), poly(vinylpyrrolidone), poly(ethylene oxide) poly(propylene oxide) polyacrylamides, cellulosics, methyl cellulose, polyacrylic acids, polyvinyl alcohols, and polyvinyl ethers and at least one cross-linking agent and then applied to the surface of the IOL insertion cartridge. The IPNs formed according to the teaching of Opolski patents are relatively rigid and inflexible due to the supporting polymers' high equivalent weights of the functional moieties. For example, Opolski provides equivalent weights in the range of about 115 to about 8700. In one embodiment Opolski provides a supporting polymer of polyacrylate and the equivalent weight of the functional moiety is in the range of about 200 to about 1000; a polyurethane supporting polymer having equivalent weights of the functional moiety in the range of about 1000 to about 8700 and a polyamine epoxide supporting polymer having equivalent weights of the functional moiety is in the range of about 100 to about 2000. Consequently, the lubricious coatings disclosed and claimed in the Opolski patents are relatively rigid and can potentially damage the IOL during the insertion process.
Therefore, it would be advantageous to provide IOL insertion cartridges with flexible, soft lubricious coatings having long shelf-lives that do not damage the IOL or transfer substantial amounts of lubricant to the IOL surfaces during insertion.